The present disclosure generally relates to active material based reversibly deployable flow trips, and in particular, in terms of one embodiment, to flow trips having active material based hinges as rotary actuators.
Airflow over, under, around, and/or through a vehicle can affect many aspects of vehicle performance including vehicle drag, vehicle lift and down force, and underhood and brake cooling. Vehicle aerodynamic drag, for instance, is inversely proportional to vehicle fuel economy. Numerous systems and devices have been created to improve vehicle aerodynamics, reduce vehicle drag, and therefore increase fuel economy. Some of the original devices to control airflow relative to a vehicle were generally of a non-adjustable geometry, location, and orientation. Such devices generally do not adapt as driving conditions change, thus the airflow relative to the vehicle cannot be adjusted with such fixed devices to better suit changes in driving conditions.
Later developments in vehicle airflow include adjustable control devices. Such devices are adjustable by connecting the devices to hydraulic, mechanical, or electrical actuators. For example, some vehicle spoilers may adjust location and/or orientation in response to an actuator signal. Such actuators, however, generally require additional components such as pistons, motors, solenoids and/or like mechanisms for activation, which increase the complexity of the device often resulting in an increased number of failure modes, increased weight, and increased maintenance and manufacturing costs.
Active materials such as shape memory alloys, piezoelectrics, magnetorheological polymers, electroactive polymers, and the like, can be used as limited displacement actuators. The use of active material actuators in place of mechanical actuators such as solenoids, servo-motors, and the like, minimizes the complexity associated with these types of actuators. Moreover, these materials generally provide lightweight alternatives, minimize packaging space, and provide lower acoustic and electromagnetic field (EMF) outputs during operation. However, these materials provide limited displacement and generally do not provide rotation directly. In order to provide large displacements required in many flow trip and other applications, known active material actuators that achieve small displacements could be actuated repetitively to incrementally, in multiple small steps, achieve the desired large displacement. The drawbacks of achieving large rotational displacements in such an incremental manner are that the active material actuators become more complex and the time required to achieve full deployment is dramatically increased
Accordingly, there is a need for an improved active material actuated flow trip. It is to be recognized that a particular advantage of active flow trips is that in their deployed state at high vehicle speeds they improve aerodynamics, thereby reducing drag and increasing fuel economy, while in their stowed state when the vehicle is either stationary or being driven at low speeds, they preserve the body lines intended by vehicle designers.